Misfolded proteins are observed in many genetic and sporadic forms of neurodegeneration and are associated with multiple neuronal disturbances. In some familial forms of disease, misfolding of the disease-related protein is due to mutations within the gene that encodes the protein. However, the mechanisms that underlie protein misfolding in other neurodegenerative diseases, in particular the sporadic, late-onset forms of these disorders, remain largely unknown. Our phenotype-driven approach has identified novel loss-of-function mutations that result in protein misfolding and neurodegeneration. In particular we have demonstrated that an editing mutation in the gene encoding alanyl tRNA synthetase (AlaRS) causes tRNA mischarging and accumulation of misfolded proteins in Purkinje cells. Importantly, also using a forward genetic approach, our laboratory has identified a novel gene, Stim, which cell-autonomously suppresses the accumulation of protein misfolding in these neurons and their subsequent degeneration. This proposal describes experiments to test the sensitivity of neurons, other than Purkinje cells, to mistranslation, via the generation of a mouse with a more severe deficiency in AlaRS editing. The function of Stim in other neurons will be tested in this model. We will also establish the role of Stim in the clearance of misfolded proteins via modulation of ubiquitin/proteasome system. Lastly, the effects of complete loss of Stim function will be assessed in mice with a conditional null mutation in this gene. Relevance of the proposed research to public health: The accumulation of abnormal proteins in neurons is associated with many human neurodegenerative disorders, including Parkinson's disease, Alzheimer's disease, Huntington's disease and ALS. The experiments outlined in this proposal will further define a novel gene that suppresses neuron death and the accompanying movement abnormalities that occur in response to the accumulation of abnormal proteins in Purkinje neurons in the cerebellum, the region of the brain that controls motor coordination. In addition, the ability of this gene to suppress neuronal dysfunction in other regions of the brain will be tested. The results from these experiments will potentially provide novel therapeutic targets for neuronal degenerative disorders.